Dimerization process for producing adiponitrile



i United States Patent 3,133,956 DEKERIZATIGN PROCESS FOR PRODUCING ADIPONITRILE Robert E. Robinson, Cincinnati, Ohio, assignor to National Distillers and Chemical Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed Dec. 2%, 1960, Ser. No. 78,828 3 Claims. (Cl. 260-4658) This invention relates to a process for the preparation of dimerized products and, more particularly, to the re ductive dimerization of alpha,beta-ethylenically unsaturated mononitriles to produce linear saturated aliphatic dinitriles. Still more particularly, this invention relates to the reductive dimerization of acrylonitrile in the pres ence of finely dispersed alkali metal to produce adiponitrile.

The dimerization of acrylonitrile to adiponitrile has been reported previously. For example, Leekley, by a process described in US. Patent 2,439,308, simultaneously dimerized and reduced acrylonitrile to adiponitrile by the action of magnesium and a promoter, such as mercuric chloride, with active hydrogen. Other known processes dimerize acrylonitrile to adiponitrile in the presence of sodium amalgam in water and of potassium amalgam in hydrochloric acid.

These processes all have the disadvantage of requiring large amounts of mercury which are cumbersome and dangerous to handle, especially when used industrially. Furthermore, commercial use of mercury is expensive.

It is an object of this invention to provide a new process for the preparation of linear saturated aliphatic dinitriles from alpha,beta-ethylenically unsaturated aliphatic mononitriles. A further object of this invention is to provide a simple, economical process for producing adiponitrile from acrylonitrile. Other objects will become apparent from the ensuing description.

These objects are accomplished by a process for the preparation of a linear saturated aliphatic dinitrile from an alpha,beta-ethylenically unsaturated aliphatic mononitrile which comprises treating the alpha,beta-ethylenically unsaturated aliphatic mononitrile in aqueous condition with finely dispersed alkali metal. The reaction may be illustrated by the following equation wherein adiponitrile is prepared from acrylonitrile and the alkali metal is sodium: 2CH =CHCN+2Na+2H O After reaction is complete, the linear saturated aliphatic dinitrile, for example, adiponitrile, is isolated by fractional distillation or by any other means known to the art.

By alpha,beta-ethylenically unsaturated aliphatic mononitrile as used herein is meant a mononitrile in which the (CN) group is attached directly to a carbon atom in an aliphatic chain, which carbon atom is in turn attached to another carbon atom by an ethylenic double bond. Examples of such compounds, to which the process of this invention applies, include acrylonitrile, methacrylonitrile, crotonitrile, alpha-propylacrylonitrile, alphaethylacrylonitrile, and the like. For convenience, this invention will be described with relation to the reaction of acrylonitrile with finely dispersed sodium, but it is not intended to be limited specifically thereto.

In the preparation of adiponitrile from acrylonitnle there should be used a relatively high proportion of acrylonitrile to alkali metal. In general, a ratio of about 1 to moles of acrylonitrile per gram atom of sodium is used, lower ratios giving considerably lower yields and higher ratios having little effect on the yield. A ratio of about 6.5 moles of acrylonitrile to one gram atom of sodium is preferred.

The process embodied herein comprises reacting aqueous acrylonitrile with an alkali metal in dispersed form in which substantially more than about 50% of the alkali metal particles are not more than about 5 microns in size, and, more preferably, not more than about two microns in size. More preferably, the process embodied herein is carried out by use of the alkali metal in the form of a dispersion in which more than of the alkali metal particles are not more than about 5 microns in size, and preferably not more than about two microns; the average particle size of the dispersion is not more than about 1.5 microns, and the dispersion is devoid of more than about 5% of alkali metal particles larger than about 3 microns in size. Optimum results are obtained by use of an alkali metal dispersion in which all or substantially all of the alkali metal particles do not exceed about two microns in size and the average particle size is l, and preferably less, micron.

For carrying out the process embodied herein, examples of the alkali metal reactant include sodium, potassium, and lithium, with sodium being preferred since it provides for excellent selectivity and yields of desired dimerized product. Also, it is cheaper and more readily available than the other alkali metals. Chemically pure sodium is not essential, however, since mixtures containing a major proportion of sodium are also useful, as are alloys of sodium and potassium, sodium and calcium, and sodium and lithium. The alkali metal dispersion employed in this invention is most conveniently, but not necessarily, made in an inert hydrocarbon or ether as a separate step preliminary to the reaction with acrylonitrile.

It has been found that yields are improved when the reaction takes place at a pH below about 9. Although satisfactory yields result when no acid is used, the inclusion in the reaction mixture of an acidic material such as hydrochloric acid, sodium bicarbonate, acetic acid, sulfuric acid, or the like has an advantageous effect. The amount of acid used may vary from about 1 to 2 equivalents per gram atom of sodium and is preferably about 1.5 equivalents per gram atom of sodium.

The aqueous acrylonitrile solution may contain from about 25 to about 95 percent of water, and preferably the reaction is run with about 75 to about percent of water in the acrylonitrile-water solution. The use of less than about 25 percent of water would enhance the formation of by-product polyacrylonitrile, while a concentration of water higher than about percent would substantially lower the yield of adiponitrile.

The reaction of acrylonitrile with finely dispersed alkali metal takes place most readily at any temperature between about 5 and 55 C. At lower temperatures it is possible that the reaction medium will freeze. The use of higher temperatures appears to offer no advantages and increases the safety hazard.

The process of the present invention can be carried out in the presence or in the absence of a solvent which is preferably an inert volatile organic material. Examples of such a solvent include hexane, benzene, dirnethyl ether, toluene, and the like, or mixtures of these.

The invention is further described by the following examples in which all parts are given by weight unless otherwise specified, but it is not intended to limit the invention specifically thereto.

Example 1 A 3-necked flask, fitted with a paddle-type stirrer, a dropping funnel, a thermometer, and a tube leading to a nitrogen bubbler system, was purged with nitrogen. and charged with 1.3 moles (69.6 parts) of acrylonitrile, 0.3 mole (25 parts) of concentrated hydrochloric acid, and 200 parts of water. The dropping tunnel was charged with parts of n-hexane and 0.2 gram atom (4.6 parts) of sodium as a 28.2 percent dispersion in mineral spirits (maximum particle size 2 microns). The magnetically agitated dispersion was added dropwise to the stirred aqueous solution over about a 100-minute period while that the sodium had a maximum particle size of 30 microns. No adiponitrile was obtained.

Example 8 To show the need for using Water with the acrylonimaintaining the reaction temp. at about to 10 C. 5 When the addition was complete, the reaction mixture was trlle, the prov-edure Of EXample 1 Was repeated, x ep steam-distilled until no further organic material was 001- that 200 parts of glacial acetic acid was substituted for lected. The residue was filtered free of polymer (6.1 the water. The yield of adiponitrile was less than 5 parts) and extracted three times with chloroform. Evappercent. oration of the solvent followed by distillation under re- 10 The results obtained in these examples are summarized duced pressure yielded 2.9 parts (27 percent, based on in the following table:

TABLE Sodium Acid Sodium Addition Acryloni- Yi0ld trile Adiponitrile, Example Par icle Amount, percent, based Gram size, maxi- Mole Amount, Times, Temp., on Sodium atom mum mi- Mole Minutes C.

CI'DIlS sodium) of adiponitrile, B.P. 105-110" C./3 mm. The 30 While there are above disclosed but a limited number product was identified by comparison of its infrared spec of embodiments of the process of the invention herein trum with that of authentic adiponitrile. It was further presented, it is possible to produce still other embodiidentified by hydrolyzing it to adipic acid which was then ments without departing from the inventive concept hereidentified by mixed melting point with a commercial speciin disclosed, and it is desired therefore that only such men of adipic acid. limitations be imposed on the appended claims as are Example 2 stated therein. The procedure of Example 1 was repeated, except that Y X 1S clamed 13: f hi h 2.6 moles of acrylonitrile was used. The yield of adiponip e ggi fg g i ggi g 3 :2 21 e g zq gg tnle was 23 Percent based on sodlum' 40 solution of acrylonitrile with an alkali metal in dispersed Example 3 form in which more than about 50 percent of the alkali Substantially the same procedure as described in Exammetal Particles are not than about 5 m pie 1 was repeated, except that sodium bicarbonate was 512% of Water m the aqueous Sohmon of used instead of hydrochloric acid. The yield of adiponiacrylommle rangmg from about to Percenttrile was 26 percent, based on sodium 2. The process as defined in cla1m 1 wherein the alkali metal is sodium, the reaction is carried out at a tempera- Example 4 ture between about 5 and 55 C., and the amount of The procedure of Example 3 was repeated, except that water in the aqueous SOlLlllOl'l Of acrylonitrile ranges from the sodium was added in 12 minutes. The yield of adiabout 75 to about 80 P p Ponitrile was 29 Percent, based on Sodiunm 3. A process for the simultaneous dimerization and E I 5 reduction of acrylonitrile to adiponitrile which comprises xamp e treating an aqueous solution of acrylonitrile with finely To illustrate the desirability of carrying out the reacdivided S0d ium in inert Volatile Organic Solvent, Said tion in an acid medium, the procedure of Example 1 was Tia-@1011 b81112 Farmed out at P above ab ut repeated, except that no acidic material was used. The 5 the sfldlum featftant belfig the form of finely yield of adiponitrile was less than 11 percent, based on d1v1ded particles of WhlCh substant ally more than about sodium 50% are not more than about 5 m1crons in size, and the Example 6 amount of water in the acrylonitrile-water solution rang- Th d f E 1 1 t d t th t ing from about 25 to about 95 percent.

e proce ure 0 xamp e was repea e excep a the temperature was maintained at about 4 to 52 C. References Cted m the file of thls Patent The yield of adiponitrile was 21 percent, based on sodium. UNITED STATES PATENTS Example 7 2,773,092 Carley et a1 Dec. 4, 1956 In order to show the eflect of the particle size of the OTHER REFERENCES sodium, the procedure of Example 1 was repeated, except Bergmann: Acetylene Chemistry, 1948, page 80. 

1. A PROCESS FOR PREPARATION OF ADIPONITRILE WHICH COMPRISES TREATING AT A TEMPERATURE ABOVE 5*C. AN AQUEOUS SOLUTION OF ACRYLONITRILE WITH AN ALKALI METAL IN DISPERSED FORM IN WHICH MORE THAN ABOT 50 PERCENT OF THE ALKALI METAL PARTICLES ARE NOT MORE THAN ABOUT 5 MICRONS IN SIZE, THE AMOUNT OF WATER IN THE AQUEOUS SOLUTION OF ACRYLONITRILE RANGING FROM ABOUT 2K TO ABOUT 95 PERCENT. 